1. Field of the Invention
The present invention relates generally to electronic inventory systems, and more particularly to the use of radio frequency identification (RFID) tags using anti-clash protocols.
2. Description of the Related Art
In modern business, maintaining an accurate inventory of merchandise is crucial. In the past, taking an inventory was an entirely manual process, and therefore slow and expensive. Modern automated inventory systems have improved the accuracy and speed of this process while reducing its cost. With the development of modem manufacturing methods, such as Just-In-Time Delivery, even faster and more accurate inventory methods are required. In some businesses, such as the baggage-handling aspect of the airline industry, inventories must be taken almost instantaneously.
Especially in the airline baggage handling industry, the need for quick and accurate inventories of bags cannot be exaggerated. In the past, the failure to match bags to passengers was merely an inconvenience. However, in the modern age of airline terrorism, the need to match passengers to bags has become a crucial safety concern. Following several airline bombings, the Commission on Aviation Safety and Security issued several recommendations to President Clinton on Sep. 5, 1996 to combat such terrorism. One of the recommendations stated: "Match passengers to their bags to ensure that the baggage of anyone who does not board the plane is removed".
One approach to electronic inventory systems is the use of RFID tags. In such systems, an RFID tag is attached to each item to be inventoried. Each tag includes a microprocessor and RF circuitry capable of responding to signals sent from a tag reader. In an ideal inventory system, each tag is assigned a unique tag identification number (Tag ID).
In one such system, the reader transmits a series of clock pulses to the tags. Each clock pulse defines a time slot. Each tag selects a particular time slot using a random number generator and then counts the received time slots. When a given tag's time slot is reached, the tag transmits its Tag ID to the reader. The reader records the received Tag IDs to create an inventory of the tags read.
This approach can suffer from a problem known as "time slot contention". Time slot contention occurs when more than one tag selects the same time slot for Tag ID transmission. When this occurs, the reader is bombarded by more than one tag transmission simultaneously. Because the tag signals interfere with each other, the reader cannot identify the tags.